Publicly own treatment works (POTW) generally cannot handle industrial wastewater, which contains high levels of contaminants that are toxic, inhibitory or recalcitrant to biological treatment (e.g. pesticides, biocides, coolants and dyestuff). Industrial waste treatment plant is used to treat the high strength and low flow industrial effluent to reduce the Chemical Oxygen Demand (COD) and the Biological Oxygen Demand (BOD) through process such as chemical oxidation prior to discharge to POTW or to watercourse.
Organic nitrogen in wastewater is usually broken up into ammonia and during the oxidation process ammonia is finally oxidised to nitrates. As a result, the presence of high nitrogen content of effluent discharge often resulted in also high nitrate nutrient content in treated water discharged. The biological process for nitrogen removal is slow and generally requires either a large area or large volume tank.
Nitrosonium ion forms unstable intermediates with aliphatic amines and amino compounds. This process can be used to remove organic nitrogen (such as in amines, amides and amino acids) from effluent as nitrogen gas prior to the oxidation process thereby lowering the nitrogen nutrient content of discharged water.
Reagents such as permanganate, chlorine gas, hypo-chloride, ozone, and ozone with ultraviolet light (UV), hydrogen peroxide and hydrogen peroxide with or without metallic ion catalysts, UV light or ozone have been used for chemical oxidation. Ozone has been used together with activated carbon in biological activated carbon (BAC) processes to oxidise complicated non-biodegradable organic contaminants to simpler molecules for biological treatment.
The activated carbon is normally used only as an absorbent for the organic contaminants. The activated carbon is used either after the oxidation process to remove any recalcitrant contaminants and oxidation by-products in a separate stage or to adsorb the organic contaminants through physical-chemical means from the fluid onto the solid carbon media before oxidising the contaminants.
The main disadvantage of ozone is the high cost and low efficiency of ozone generating equipment. UV activated process requires large reactor size to achieve sufficient contact resulting in high capital cost. The efficiency of UV treatment is very dependent on the turbidity of the water and any other hindrances of the transmission of UV light to the water. Hydrogen peroxide with dissolved iron salts as in Fenton's reagent requires low pH (2-3) for oxidation and neutralisation (5.5-9) before the water can be disposed. Large amount of bulky ferric hydroxide precipitate that has to be removed is also produced by the activation with metallic ions.
Accordingly there has been a need for a process of treating aqueous liquid which may overcome some if not all the above-cited problems. Such a process is being provided by the present invention.
The present invention consists of certain novel features and iii combinations of parts hereinafter fully described and illustrated in the accompanying description, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the scope of the invention, or sacrificing any advantage of the present invention.